The present invention relates to flaw detection methods and apparatus and, more particularly, to a method and apparatus for inspecting the threads of the pin and box ends of drill collars, drill pipe and the like for defects.
A search of the prior art failed to uncover any prior art reference which discloses the flaw detection method and apparatus of the present invention. Several prior art patents were uncovered which disclose various devices for inspecting the interior of hollow or tubular members as exemplified by the following U.S. Patents:
U.S. Pat. No. 3,371,176
U.S. Pat. No. 3,541,976
U.S. Pat. No. 2,682,032
U.S. Pat. No. 3,285,122
In the oil and gas well drilling arts, the drill string used for boring the well is made up of a heavy drill bit and a number of drill collars, reamers and stabilizers threaded together in end-to-end relation. Because of the heavy stresses placed on the threaded joints between each of these elements during drilling, as well as the high fluid pressures in the borehole and within these drilling elements, it is important to periodically check the integrity of the threads of each box and pin as the drill collars and other drill elements are made up and run into the hole or as they are pulled from the hole. Weekly inspections or inspections approximately every 200 hours are not an uncommon requirement.
Failure of a threaded joint during drilling is, of course, costly and time-consuming since it requires interruption of drilling to pull the entire drill string from the borehole and replace the defective drill collar or other defective element of the drill string.
It is known in the drilling art to perform nondestructive inspection of the threads at the ends of drill collars and drill pipe sections at the well drilling site. One method frequently employed for performing such inspection is known as the "ZYGLO" or "blacklight" process described, for example, in U.S. Pat. No. 2,259,400, the details of which are incorporated herein by reference. Generally speaking, this process involves treating the thread surfaces with a fluorescent solution which penetrates flaw openings. The fluorescent solution is then wiped from the surfaces to be inspected and when such surfaces are exposed to ultraviolet radiant energy, any fluorescent solution seeping from the flaw openings exhibits a distinctive and vivid appearance from normal surfaces without flaws.
In the field, the most common technique for performing this inspection process is to spray, brush or otherwise coat the pin and box end thread surfaces of the drill collar with a fluorescent solution and, thereafter, wipe away the excess. The person performing the inspection then drapes a dark cloth, such as a black blanket, over himself and the end of the drill collar to be inspected. Using a portable ultraviolet or "black light" held in one hand, the inspector visually observes all the threaded surfaces of the pin and box ends of the drill collar. This inspection procedure is not only disadvantageously inefficient, cumbersome and time-consuming, but is a rather unpleasant task for the inspector, particularly when the inspection is performed in the field during hot weather.